1. Field of the Invention
The present invention relates to a belt for a continuously variable transmission, which is wound around a drive pulley and a driven pulley for transmitting a driving force between both the pulleys, and which comprises a metal ring assembly formed of a plurality of endless metal rings laminated one on another, and a large number of metal elements each having a ring slot into which the metal ring assembly is fitted.
2. Description of the Related Art
As shown in FIG. 8, the metal elements 32 are supported on the metal ring assemblies 31, 31 which are fitted into the ring slots 35, 35. If the metal elements 32 are inclined forwards in a travel direction, rear ends a of saddle faces 38L, 38L in the travel direction abut against inner peripheral surfaces of the metal ring assemblies 31, 31, and front ends of the lower faces 38U, 38U of an ear abut against the outer peripheral surfaces of the metal ring assemblies 31, 31. For this reason, there is a possibility that a large stress OH (Hertz's stress) is generated at such abutment portions and as a result, the metal ring assemblies 31, 31 are worn. The forward inclination of the metal elements 32 in the travel direction is caused by a tangent frictional force F received by the metal elements 32 at their contact faces with the pulleys, and an urging force between the metal elements 32, and is particularly significant at an exit portion of the driven pulley. The reason will be described below.
As can be seen from FIG. 7, a moment generated in a direction of an arrow M by the tangent frictional force F acts to incline the metal elements 32 forwards in the travel direction about a swinging center C. On the other hand, a radial frictional force μE generated by the urging force E between the metal elements 32 generates a moment in a direction of an arrow M′ on the metal elements 32. This moment acts to incline the metal elements 32 rearwards in the travel direction about the swinging center C.
It is known that the tangent frictional force F received by the metal elements 32 from the pulleys 6 and 11 is large at the exit portions of the drive pulley 6 and the driven pulley 11 as shown in FIG. 9A, and its value reaches four times a value provided when it is supposed that the tangent frictional force F has been averagely distributed over the entire wound regions of the pulleys 6 and 11. In addition, as shown in FIG. 9B, the urging force between the metal elements 32 has a larger value at the exit portion of the drive pulley 6, but assumes 0 (zero) at the exit portion of the driven pulley 11. Therefore, the metal elements 32 are liable to be inclined forwards in the travel direction to the largest extent at a location where the tangent frictional force F inclining the metal element 32 forwards in the travel direction is largest and the urging force E inhibiting the forward inclination of the metal element 32 in the travel direction is 0 (zero), i.e., at the exit portion of the driven pulley 11 (see FIG. 10).
For this reason, when the metal elements 32 are inclined largely forwards in the travel direction at the exit portion of the driven pulley 11, the following problem is encountered: The rear ends a of the saddle faces 38L, 38L of the metal element 32 and the front ends b of the lower faces 38U, 38U of the ear as viewed in the travel direction strongly abut against the inner and outer peripheral surfaces of the metal ring assembly 31, respectively (see FIG. 8) and as a result, the metal ring assemblies 31, 31 are worn by a stress σH generated at such abutment portions.
There are conventionally known metal elements which are described in Japanese Utility Model Application Laid-open Nos. 59-79653 and 63-17353, Japanese Patent Application Laid-open No. 6-10993 and Japanese Utility Model Application Laid-open No. 60-107444, and which have a feature in shape of a saddle face against which an inner peripheral surface of a metal ring assembly abuts.
Belts designed so that the rolling of a metal element is inhibited to enhance the durability of a metal ring assembly, are conventionally known from Japanese Patent Publication No. 2-19338, Japanese Patent Application Laid-open No. 7-12177 and Japanese Patent Publication No. 2,617,784.
In the belt described in Japanese Utility Model Application Laid-open No.59-79653, opposite edges of a saddle face of the metal element in a travel direction are smoothly chamfered. In the belt described in Japanese Utility Model Application Laid-open No.63-17353, a stepped protrusion is formed at a central portion in a travel direction of the saddle face of the metal element, and an arcuate face having a radius equal to a minimum winding radius of the metal ring assembly is formed on top of the protrusion. The purpose of this arrangement is not described clearly in the specification, but it seems that the purpose is to alleviate the strong abutment between the opposite ends of the saddle face in the travel direction and the inner peripheral surface of the metal ring assembly at the portions of the belt for continuously variable transmission which are wound around the pulleys. In these belts, the shapes of the saddle faces are symmetrical longitudinally in the travel direction and for this reason, it is difficult to effectively alleviate the Hertz's stress generated by the abutment between the opposite ends of the saddle face in the travel direction and the inner peripheral surface of the metal ring assembly.
In the belts described in Japanese Patent Application Laid-open No.6-10993 and Japanese Utility Model Application Laid-open No.60-107444, the longitudinal shapes of the saddle face of the metal element are formed asymmetrically in such a manner that the rear portion of the saddle face in the travel direction is lower in height level than the front portion in the travel direction, for the purpose of preventing the inclination of the metal element in the longitudinal direction by a pitching moment. These belts suffer from a problem of an increase in processing cost for the metal element, because the shape of the saddle face is complicated.
The belts described in the above Japanese Patent Publication Nos. 2-19338 and 7-12177, and Japanese Patent Publication No. 2,617,784 are for suppressing a rolling of the metal elements, and cannot solve the problem of wear in the metal ring assemblies due to a pitching of the metal elements.
The present invention has been accomplished with the above circumstance in view, and it is an object of the present invention to prevent the wear of the metal ring assembly due to the inclination of the metal element without increasing of the processing cost for the metal element.
To achieve the above object, according to a first feature of the present invention, there is provided a belt for a continuously variable transmission, which is wound around a drive pulley and a driven pulley for transmitting a driving force between both the pulleys, the belt comprising a metal ring assembly formed of a plurality of endless metal rings laminated one on another, and a large number of metal elements each having a ring slot into which the metal ring assembly is fitted, wherein an endless resilient member which is elastically deformable radially is disposed between a radially outer edge of the ring slot in the metal element and a radially outer peripheral surface of the metal ring assembly.
With the above arrangement, the endless resilient member which is deformable radially is disposed between the radially outer edge of the ring slot in the metal element and the radially outer peripheral surface of the metal ring assembly. Therefore, when the metal elements are inclined in such a manner that they are fallen forwards in the vicinity of an exit portion of the driven pulley of the metal belt type continuously variable transmission, the metal ring assembly can be prevented from strongly interfering with the radially outer and inner edges of the ring slot in the metal ring assembly by a buffering action provided when the resilient member is deformed radially, thereby preventing wear of the metal belt to enhance the durability thereof. Moreover, the belt is of a simple structure in which the resilient member is only added without subjecting the metal element to a special processing, and hence, the belt can be realized at an extremely low cost.
According to a second feature of the present invention, the peripheral length of the radially inner peripheral surface of the resilient member is set longer than that of the radially outer peripheral surface of the metal ring assembly.
With the above arrangement, the peripheral length of the radially inner peripheral surface of the resilient member is longer than that of the radially outer peripheral surface of the metal ring assembly, and hence, a clearance can be created between the resilient member and the metal ring assembly, to thereby further increase the buffering action of the resilient member.